Optimizing the design ammonia loading rate of submerged attached-growth reactors in warm and cold conditions

Lagoons are commonly used to treat wastewater in North America – primarily by small towns and municipalities. Ammonia in lagoon effluent is known to be toxic to aquatic environments. The ability of lagoons to remove ammonia from wastewater is highly temperature-dependent. Total Ammonia Nitrogen (TAN) -related regulatory limits for lagoon effluent are increasingly stringent. Where additional ammonia removal from lagoon effluent is required, post-lagoon nitrification reactors might be used, such as the Submerged Attached Growth Reactor (SAGR). The SAGR is a technology owned by Nexom. It is sized using a typical design maximum TKN loading rate (per unit volume of the SAGR). Historic studies have shown that nearly full TAN and TKN removal can be consistently achieved in SAGRs sized using these design parameters at very low sustained water temperatures of even less than 1°C. Some have shown that this is even possible with reduced SAGR volume. This suggests that the design ammonia loading rate values might be increased to optimize the SAGR size. The current typical design loading rate is 12.8 g-TKN/m³ˑday (0.8lb-TKN/1000ft³ˑday). The chapters in this thesis show that a value of 31.1 g-TKN/m³ˑday (1.96 lb-TKN/1000ft³ˑday) might be used in ‘warm’ conditions with lagoon effluent temperature greater than 20°C, and a value of 21.9 g-TKN/m³ˑday (1.38lb-TKN/1000ft³ˑday) might be used in moderately cold conditions where lagoon effluent temperature might drop to between 3 and 4°C in winter. The first pilot study, completed in the summer of 2022, observed SAGR operation at influent temperatures greater than 20°C and loaded at an average loading rate of at least 31.1 g-TKN/m³ˑday (1.96 lb-TKN/1000ft³ˑday). The pilot reactor recorded nearly 100% removal of TAN consistently during stable operation. The second pilot study, completed in the winter of 2022/2023, observed SAGR operation at influent temperatures below 4°C, and loaded at an average loading rate of 21.9 g-TKN/m³ˑday (1.38lb-TKN/1000ft³ˑday). The pilot reactor recorded nearly 100% removal of TAN consistently during stable operation. The results of these studies indicate that SAGRs might be designed in the future with significant reductions in footprint and, therefore, significant reductions in cost to the end user, many of which are rural municipalities struggling to meet regulatory limits. The consequences of these design size reductions will include increased access to suitable wastewater treatment technology and, therefore, higher quality lagoon discharges to surface water bodies on a broad scale .

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